1. Field of the Invention
The present invention relates to rotating magnetic disk drives, and more particularly, to a method for determining repeatable runout written to a servo track during a servowriting process for accurate track following relative to a concentric track center.
2. Description of the Prior Art
Repeatable runout (RRO) in a disk drive results from imperfections, with respect to a perfect circle, in the location of servo information along a track on a disk surface in the disk drive. Due to disk spindle rotation, the servo imperfections due to RRO are periodic having a fundamental frequency that is equal to the spindle rotation frequency. The RRO imperfections are relatively static over time and the effect of the RRO may be attenuated by measuring the RRO during manufacturing and using the RRO measurements in a head-position servo loop to compensate for the RRO effect.
However, accurate RRO measurements may be difficult to obtain. The head-position servo loop may not be able to track the imperfections or may prevent convergence on cancellation values in a timely and cost effective manner.
Accordingly, there exists a need for technique for determining RRO cancellation values without unnecessarily increasing manufacturing costs or significantly decreasing manufacturing throughput. The present invention satisfies these needs.